Vehicle control system and method

ABSTRACT

Aspects of the present invention relates to a vehicle control system ( 1 ) for controlling a vehicle transfer case ( 3 ). The transfer case ( 3 ) is operable in a high range and a low range. The vehicle control system ( 1 ) includes a selection means ( 21 ) for selecting first and second control strategies for the transfer case. The first and second control strategies are based on an activation time of the selection means ( 21 ). A further aspect of the present invention relates to a vehicle control system ( 1 ) for implementing a deferred transfer case range change. The present invention also relates to a vehicle ( 5 ) and a related method of operating a vehicle control system ( 1 ).

TECHNICAL FIELD

The present invention relates to a vehicle control system; a method ofcontrolling a transfer case; and a vehicle.

BACKGROUND OF THE INVENTION

It is known to provide vehicles with a transfer case (also referred toas a reduction gearbox) to provide additional drive ranges. The transfercase is typically coupled to an output shaft from a transmission and, ina four-wheel drive vehicle, provides drive to the front and rear axlesvia front and rear propeller shafts. The torque delivered to the frontand rear axles can be the same (i.e. 50:50 distribution) or different.The transfer case can also include a reduction gear set, for example ahelical reduction or an epicyclic reduction gear set, to provide highand low drive ranges. The high range can provide a 1:1 ratio (i.e.direct drive) and the low range can provide a reduction gearing, forexample 2.69:1.

The transfer case has particular application in off-road vehicles wherethe low range can increase the torque delivered at the wheels andprovide improved low-speed control. High range should be used for allnormal road driving and also for off-road driving across dry, levelterrain. Low range should only be required where low speed maneuveringis necessary, such as reversing a trailer, negotiating steep slipperysurfaces or boulder strewn terrain. Low range should also be used forextreme off-road conditions where progress in high range cannot bemaintained. Low range should not normally be used for normal roaddriving.

The transfer case can also include a synchroniser to enable dynamicrange changes while the vehicle is travelling (referred to asshift-on-the-fly or shift-on-the-move control). By way of example, thetransfer box can facilitate range changes when the vehicle is moving,within set limitations as follows:

-   -   High to Low—at speeds not exceeding 10 mph (16 km/h)    -   Low to High—at speeds not exceeding 30 mph (48 km/h).        If no synchroniser is fitted, static range changes are typically        implemented with the vehicle stationary. The transfer case range        changes from low to high are referred to herein as upshifts, and        the transfer case range changes from high to low are referred to        herein as downshifts. The transfer case can also be moved into a        neutral position for towing the vehicle.

At least in certain embodiments the present invention attempts toovercome or ameliorate at least some of the limitations or problemsassociated with known transfer cases.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a vehicle control system; amethod of controlling a transfer case; and a vehicle.

According to an aspect of the present invention there is provided avehicle control system for controlling a vehicle transfer case operablein a high range and a low range; the vehicle control system comprisingselection means for selecting first and second control strategies forsaid transfer case; wherein the selection means is operable to selectsaid first and second control strategies based on an activation time ofsaid selection means. The transfer case selection means enablesselection of either the first control strategy or the second controlstrategy based on the activation time. At least in certain embodimentsof the present invention, the selection means can facilitate control ofthe transfer case and reduce the number of vehicle controls required.The vehicle control system can be in the form of a transfer case controlmodule. The transfer case control module can comprise said transfer caseselection means.

The first control strategy can be selected if the activation time isless than a predefined time threshold. The second control strategy canbe selected if the user activation time is greater than said predefinedtime threshold. The selection means could enable selection of additionalcontrol strategies. For example, a third control strategy can place thetransfer case in a neutral position for towing. The third controlstrategy can, for example, be selected to place the transfer case inneutral when the activation time is greater than a neutral timethreshold.

The first control strategy and/or the second control strategy canimplement a transfer case range change. The transfer case range changecan be an upshift (i.e. a change from the low range to the high range);or a downshift (i.e. a change from the high range to the low range). Theperformance of an upshift or a downshift can be dependent on the currentoperating range of the transfer case. If the transfer case is operatingin the high range, the range change can be a downshift to engage the lowrange. Conversely, if the transfer case is operating in the low range,the range change can be an upshift to engage the high range. The controlsystem can be configured to determine and implement the appropriaterange change automatically based on the current operating range of thetransfer case.

The selection means can be in the form of a button, a switch, a lever, apaddle, a capacitive switch, an actuator (physical or virtual), atouchscreen interface, or other types of human machine interface. Theactivation time is the time period for which the range selection meansis activated. For example, the activation time can be the period of timea button is depressed.

The range selection means can output a range change signal. The transfercase can be configured to implement the range change in dependence onthe range change signal.

The first control strategy can implement a concurrent range change. Whenthe first control strategy is selected, the range selection means canoutput said range change signal concurrent with activation of the rangeselection means.

The second control strategy can implement a deferred transfer case rangechange. The range selection means can defer output of said range changesignal after activation of the range selection means. The selection ofthe second control strategy can prime the control system to perform thetransfer case range change. Alternatively, or in addition, the secondcontrol strategy can implement a differential lock function. In thisarrangement, the differential would lock when the second controlstrategy is selected. This function could be used in place of, or inaddition to a dedicated selection means for locking the differential.

The control system can be configured to display the activation time ofthe selection means. The control system can be configured to displayfirst and second graphical indicia representing the respective first andsecond control strategies. The control system could be configured todisplay (or highlight) either the first graphical indicia or the secondgraphical indicia to indicate whether the first or second controlstrategy would be selected based on the activation time of the selectionmeans.

According to an aspect of the present invention there is provided avehicle control system for controlling a vehicle transfer case operablein a high range and a low range; wherein the control system is operableto implement a deferred transfer case range change. The control systemcan be primed to implement the deferred range change.

The control system can be configured to implement the deferred transfercase range change when one or more vehicle operating conditions aresatisfied. The vehicle operating condition(s) can be pre-defined oruser-specified. The vehicle operating conditions can relate to vehicledynamics.

The one or more vehicle operating conditions can comprise vehicle speedand/or vehicle acceleration. The deferred transfer case range change canbe implemented when the vehicle speed exceeds a speed threshold. Thespeed threshold can be pre-defined; or the speed threshold can beuser-defined. The control system can be configured to implement atransfer case upshift when the vehicle speed increases above a firstspeed threshold. The range selection means can be configured toimplement a transfer case downshift when the vehicle speed decreasesbelow a second speed threshold. The first and second speed thresholdscould be the same. Alternatively, the first speed threshold can be lessthan the second speed threshold. In an alternative, the second speedthreshold can be less than the first speed threshold.

The deferred transfer case range change can be implemented when thevehicle acceleration exceeds a pre-defined acceleration threshold. Thecontrol system can be configured to implement a transfer case upshiftwhen the acceleration exceeds a threshold.

The one or more vehicle operating conditions can comprise actuation of akickdown switch on a throttle pedal. The control system can beconfigured to implement a transfer case upshift when the kickdown switchis actuated.

The one or more vehicle operating conditions can comprise an operatingrange of the transfer case. As outlined herein, the type of range change(i.e. an upshift or a downshift) can be performed in dependence on thecurrent operating range.

The transfer case can be operated in conjunction with a vehicletransmission. The vehicle transmission typically provides a plurality offorward drive gears and a reverse drive gear. The one or more vehicleoperating conditions can comprise an operating range of the vehicletransmission. The deferred transfer case range change can be implementedwhen the vehicle transmission engages neutral. The control system can beconfigured automatically to implement the range change when neutral isengaged by the vehicle transmission.

The one or more vehicle operating conditions can comprise a drivertorque request. The control system can be configured to implement therange change when the driver torque request is substantially zero (i.e.the throttle pedal is not depressed); or is below a torque requestthreshold. The control system can be configured automatically to controlthe torque request, for example to reduce the powertrain torque duringthe range change.

The control system can be configured to implement the deferred rangechange after a pre-defined period of time has elapsed.

The control system can define a minimum activation threshold. The firstcontrol strategy can be selected only when the user activation time isgreater than said minimum activation threshold. The control system candefine a maximum activation threshold. The control system can be resetwhen the user activation time is greater than said minimum activationthreshold. Specifically, the control system can be reset to cancel thesecond control strategy, thereby cancelling the deferred transfer caserange change.

The control system can be operable to cancel the deferred transfer caserange change when an activation procedure is repeated. For example,activation of the selection means can be repeated to cancel the secondcontrol strategy. The control system can be reset to cancel the deferredtransfer case range change.

According to a further aspect of the present invention there is provideda method of controlling a vehicle transfer case operable in a high rangeand a low range; the method comprising selecting first and secondcontrol strategies for said transfer case based on an activation time ofa selection means. The activation time can correspond to a period oftime for which a selection means is activated.

The method can comprise selecting the first control strategy if theactivation time is less than a predefined time threshold. The method cancomprise selecting the second control strategy if the user activationtime is greater than said predefined time threshold.

When the first control strategy is selected, the method can compriseimplementing the transfer case range change concurrently with activationof the selection means.

When the second control strategy is selected, the method can comprisedeferring implementation of the transfer case range change. The methodcan comprise priming the vehicle control system when the second controlstrategy is selected.

According to an aspect of the present invention there is provided amethod of controlling a vehicle transfer case operable in a high rangeand a low range; the method comprising priming a vehicle control systemto implement a deferred transfer case range change.

The method can comprise implementing the deferred transfer case rangechange when one or more vehicle operating conditions are satisfied. Theone or more vehicle operating conditions can comprise vehicle speedand/or vehicle acceleration.

The method can comprise implementing the deferred transfer case rangechange when the vehicle speed exceeds a predefined speed threshold. Thespeed threshold can be pre-defined; or the speed threshold can beuser-defined. The method can comprise implementing a transfer caseupshift when the vehicle speed increases above a first speed threshold.The method can comprise implementing a transfer case downshift when thevehicle speed decreases below a second speed threshold. The first andsecond speed thresholds can be the same. Alternatively, the first speedthreshold can be less than the second speed threshold. In analternative, the second speed threshold can be less than the first speedthreshold.

The method can comprise implementing the range change when the vehicleacceleration exceeds a pre-defined acceleration threshold. The methodcan, for example, comprise implementing an automated transfer caseupshift when vehicle acceleration exceeds said acceleration threshold.

The one or more vehicle operating conditions can comprise an operatingrange of the transfer case. The method can comprise implementing atransfer case upshift to the high range if the transfer case isoperating in a low range. Conversely, the method can compriseimplementing a transfer case downshift to the low range if the transfercase is operating in a high range.

The method can comprise performing a transfer case upshift in dependenceon actuation of a kickdown switch on a throttle pedal.

The one or more vehicle operating conditions can comprise the selectedrange in the vehicle transmission. The method can comprise implementingthe deferred transfer case range change when the vehicle transmissionengages neutral.

The method can comprise implementing the deferred range change after apre-defined period of time has elapsed.

The vehicle control system described herein can take the form of acontrol apparatus, for example comprising one or more control modules.The control modules can each contain one or more processors which canfunction independently of each other or in parallel. The control modulescan be disposed in a vehicle systems architecture, for examplecommunicating with each other over a network.

The methods described herein can be computer-implemented, for example ona computational apparatus or computer comprising one or moremicroprocessors. According to a yet further aspect of the presentinvention there is provided a computer program product comprising acomputer readable storage medium including computer readable programcode, where the computer readable program code when executed on acomputer causes the computer to perform the method(s) described herein.

The term processor used herein is to be understood as covering bothsingle processors and multiple processors. For example, the processingsteps described herein could be performed by a single processor; orcould be performed by separate processors. The processors could, forexample, be provided in different control modules making up a vehiclecontrol system. Thus, the vehicle control system can be integrated intoa vehicle systems architecture incorporating one or more control modulesin communication with each other over a network.

Within the scope of this application it is expressly envisaged that thevarious aspects, embodiments, examples and alternatives set out in thepreceding paragraphs, in the claims and/or in the following descriptionand drawings, and in particular the individual features thereof, may betaken independently or in any combination. Features described inconnection with one embodiment are applicable to all embodiments, unlesssuch features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described, by way ofexample only, with reference to the accompanying figures, in which:

FIG. 1 shows a schematic representation of a vehicle incorporating avehicle control system in accordance with an embodiment of the presentinvention;

FIG. 2 shows a first block diagram illustrating operation of the vehiclecontrol system;

FIG. 3 shows a first flow chart showing implementation of the controlstrategy illustrated in FIG. 2;

FIG. 4 shows a second block diagram illustrating operation of thevehicle control system in dependence on a trigger event;

FIG. 5 shows a second flow chart showing implementation of the controlstrategy illustrated in FIG. 4;

FIGS. 6A and 6B show respective third and fourth block diagramsillustrating operation of the vehicle control system when a trailer isdetected;

FIG. 7 shows a fifth block diagram illustrating operation of the vehiclecontrol system in dependence on vehicle speed and acceleration;

FIG. 8 shows a third flow chart showing implementation of the controlstrategy illustrated in FIG. 7;

FIG. 9 shows a fourth flow chart showing implementation of the controlstrategy upon engine ignition;

FIG. 10 shows a sixth block diagram illustrating operation of thevehicle control system in dependence on a selected vehicle operatingmode; and

FIG. 11 shows a fifth flow chart showing implementation of the controlstrategy illustrated in FIG. 10.

DETAILED DESCRIPTION OF AN EMBODIMENT

A vehicle control system 1 incorporating a transfer case control module(TCCM) 2 in accordance with an embodiment of the present invention isdescribed herein with reference to the accompanying Figures. The TCCM 2is operable to control a transfer case 3 of a vehicle 5 to changebetween high and low ranges.

With reference to FIG. 1, the TCCM 2 and the transfer case 3 areinstalled in the vehicle 5. The vehicle 5 has two front wheels W1, W2and two rear wheels W3, W4 and a drive torque can be selectivelydelivered to each of the wheels W1-4 (i.e. the vehicle has four wheeldrive 4WD). An internal combustion engine E (shown in phantom in FIG. 1)is provided for delivering torque to the wheels W1-4. The invention canalso be implemented in a vehicle 5 utilising one or more electricmachines to drive the wheels W1-4, for example a hybrid electric vehicle(HEV) or an electric vehicle (EV). The present invention could beapplied in other All-Wheel Drive (AWD) vehicles, for example vehiclescomprising six wheels.

The transfer case 3 is mounted to a transmission 7 in the vehicle 5. Thetransfer case 3 enables a transfer of drive from a single transmissionoutput to a twin output to deliver torque to the front wheels W1, W2 viaa front drive (propeller) shaft 9 and front differential 11, and to therear wheels W3, W4 via a rear drive (propeller) shaft 13 and reardifferential 15. The transfer case 3 comprises a centre differential toallow a speed difference across the front and rear drive shafts 9, 13.In order to aid off road traction, the transfer case 3 comprises areduction gear set to provide a twin speed transfer case 3 selectivelyoperable in a high range (direct drive) and a low range (reductiondrive). The transfer case 3 comprises a servo actuator, such as anelectromagnetic machine, for changing between the high range and the lowrange. The operation of the servo actuator is controlled by the TCCM 2.The servo actuator can be disposed inside the transfer case 3 orexternally of the transfer case 3.

The transfer case 3 can optionally comprise a synchroniser to allow adynamic change between said high and low ranges. The synchroniser allowsthe transfer case 3 to complete shifts between the high and low ranges(both from the high range to the low range and vice versa) whilst thevehicle 5 is moving (referred to as shift-on-the-fly orshift-on-the-move control), thereby avoiding the need for the driver tostop the vehicle 5 to complete the range change. The synchronisermatches the rotational speed of the output from the transfer case 3 withthe internal rotational speed of the transfer case 3. The transfer case3 is directly coupled to the front and rear drive shafts 9, 13 and,therefore, is determined by the vehicle (road) speed. The rotationalspeed of an input shaft for the transfer case 3 should be as close tozero as possible to allow the transfer case 3 to synchronise with thetransmission 7 (approximate zero velocity difference). The transmission7 must select neutral to allow the speed of the input shaft to thetransfer case to decrease sufficiently before the transfer case 3 shiftsbetween said high and low ranges. For example, the range change can beperformed when the input shaft speed is approximately 100 rpm. Thesynchroniser can then increase the rotational speed of the transfer case3 to match the vehicle speed so the transfer case 3 and the output shaftfrom the transmission 7 are rotating at the vehicle speed. The shift to“drive” and re-engagement of gear is then handled by a torque converterin terms of engine speed synchronisation to vehicle speed.

In prior art arrangements, the driver must first engage neutral in thetransmission 7 before changing between high and low transfer caseranges. If the transfer case 3 does not include a synchroniser, onlystatic changes can be performed. In other words, the vehicle 5 must bestopped before the transfer case 3 can change between said high and lowranges. The present invention has applications in transfer cases 3either with or without a synchroniser and the control strategiesimplemented to perform static and dynamic shifts are described herein.At least in certain embodiments, the vehicle control system 1 canimplement an autonomous or semi-autonomous transfer case range change.

A range change selector 21 is provided to enable the driver to request arange change. When activated, the range change selector 21 generates arange change request signal which is published to a vehiclecommunication network 23. In the present embodiment, the range changeselector 21 comprises selection means in the form of a button which canbe depressed by the driver to select a range change. It will beappreciated that the selection means could take other forms, such as aswitch, a lever, a capacitance sensor, or a virtual selector displayedon a touchscreen interface. In the present embodiment the selectionmeans also comprise a set of steering wheel controls which provideduplicate controls. The steering wheel controls allow the driver toimplement a range change without taking their hands off the steeringwheel. Alternatively, or in addition, the selection means could bedisposed on the dashboard or centre console.

The TCCM 2 receives data signals from other on-board electronic modulesover the vehicle communications network 23. In particular, the TCCM 2 isconfigured to receive vehicle operating parameters indicating thedynamic status of the vehicle and its various systems. The TCCM 2communicates with the other modules over the communications network 23to implement a control strategy for implementing a transfer case rangechange. The TCCM 2 receives data from, and publishes data to thecommunication network 23. The TCCM 2 can, for example, publish one ormore of the following network signals to the communication network 23:

-   -   (a) a change notification signal for indicating that a range        change has been requested, for example in dependence on receipt        of the range change request;    -   (b) a change identification signal for indicating that the        attempted range change is a static change or a dynamic change;    -   (c) a change initialisation signal for initialising the range        change; and    -   (d) a range change completion signal for indicating that the        range change has been completed; or    -   (e) any other state which may require a different reaction from        other modules on the vehicle 5.

The TCCM 2 accesses vehicle operating parameter(s) over thecommunication network 23 to determine the current status of vehiclesystems and/or the dynamic operating parameters of the vehicle 5. Forexample, the TCCM 2 accesses vehicle speed data and modifies the changeidentification signal to indicate whether the attempted range change isstatic or dynamic. If the transfer case 3 does not include asynchronizer, the TCCM 2 determines that the range change is not viableif the vehicle 5 is moving and outputs a notification to the instrumentpack control module 33 to inform the driver that the requested rangechange is not possible, optionally also indicating that the vehicle 5should be brought to rest. Equally, if the transfer case 3 comprises asynchronizer but the TCCM 2 determines that the vehicle speed is above apredefined range change threshold, a notification is output to theinstrument pack control module 33 to inform the driver that therequested range change is not possible, optionally also indicating thatthe vehicle 5 should be slowed.

The vehicle modules which operate to implement a successful range changeinclude:

-   -   a transmission control module (TCM) 25 for controlling the        transmission 7;    -   an anti-lock braking system (ABS) control module 27 for        controlling the front and rear friction brakes;    -   a powertrain control module (PCM) 29 for controlling the        powertrain;    -   a gear selector module (GSM) 31 for controlling driver selection        of gears;    -   an instrument pack control module (IPCM) 33 for controlling the        output of information to the driver;    -   an advanced terrain control module (ATCM) 35 for controlling        dynamic operating parameters of the vehicle 5.

The control strategy implemented by the TCCM 2 is illustrated in a firstblock diagram in FIG. 2. A range change request signal is received fromthe range change selector 21 in response to a driver request (A1). Uponreceipt of the range change request signal over the communicationsnetwork 23, the TCM 25 and/or the GSM 31 request neutral in thetransmission 7; the GSM 31 inhibits gear selection; the PCM 29 inhibitsthrottle pedal input; and the ABS control module 27 applies the brakesand/or controls wheel speed (A2). The transfer case 3 then performs therange change (A3). The TCM 25 engages an appropriate gear; the GSM 31permits gear selection; and the PCM 29 enables throttle pedal inputs(A4). The range change is then complete (A5).

At least in certain embodiments, the TCCM 2 is operative to reduce thedriver input to implement a range change through implementing certainconditions when the range change selector 21 is activated. As describedherein, upon receipt of the range change request signal over thecommunications network 23, the TCCM 2 will check vehicle operatingparameters to determine if a range change is viable. If the parameterscomply with predefined conditions, the TCCM 2 will output the changenotification signal to indicate that the range change has beenrequested. The GSM 31 comprises a selector, such as a gear lever,paddle(s) or a rotary dial, for selection of gears in the transmissionby the driver. The GSM 31 could be provided with duplicate controls, forexample steering wheel mounted paddles together with a lever.

The electronic modules are configured to control the associated systemsbased on the network signal(s) output from the TCCM 2. Upon receipt ofthe change notification signal, the relevant vehicle modules areoperative to perform a sequence of events to allow the transfer case 3to perform the range change successfully. As illustrated in FIG. 3, whenthe change notification signal is received over the communicationsnetwork 23, the electronic modules implement the following controlstrategy:

-   -   a. The TCM 25 controls the transmission 7 to engage neutral        [STEP 6] which is a requirement for range change.    -   b. The ABS control module 27 engages the vehicle brakes or        control wheel speed [STEP 4] to prevent vehicle rollaway.    -   c. The PCM 29 inhibits throttle input [STEP 7].    -   d. The GSM 31 locks or inhibits shifting [STEP 5].    -   e. The IPCM 33 outputs a driver notification indicating the        status of the range change [STEP 8].

Only once these steps have been successfully completed does the TCCM 2execute the range change. The control strategy ensures that the eventsare performed in a timed order to eliminate the chances of the vehicleoperating in an unexpected manner, for example rolling away during therange change. The static shift strategy is implemented for all rangechanges performed by a transfer case 3 which does not have asynchroniser; and also for a transfer case 3 having a synchroniser whenthe vehicle 5 is stationary. The control strategy will now be describedin more detail for both static and dynamic shifts.

Static Shifting (Vehicle Stationary)

The control strategy for implementing a static range change will now bedescribed with reference to a first flow chart 100 shown in FIG. 3. Thecontrol strategy is the same irrespective of whether the range change isfrom a low range to a high range or vice versa.

-   -   i. The TCCM 2 receives a range change request from the range        change selector 21 [STEP 1]. The TCCM 2 assesses whether the        current vehicle state is suitable to perform a range change. If        the vehicle 5 is not in a suitable state, for example the        vehicle 5 is moving, the IPCM 33 outputs a message [STEP 3] for        display on the instrument cluster advising the driver that the        range change cannot be performed. If the TCCM 2 determines that        a range change is possible, the change notification signal is        output to the communications network 23. In practice, the change        notification signal is generated by changing the value of a        communications signal [STEP 2] to indicate that the vehicle is        completing a static range change.    -   ii. The ABS Module 27 receives the change notification signal        over the communication network 23 and engages a hill hold        function [STEP 4] to prevent the vehicle 5 from rolling away        during the range change, for example when neutral is selected in        the transmission 7. The ABS module 27 then publishes a hill hold        notification to the communication network 23.    -   iii. Upon receipt of the change notification signal, the GSM 31        locks the gear selector [STEP 5], either mechanically or through        software, to prevent the driver from engaging a gear in the        transmission 7 during the range change. The GSM 31 publishes a        gear selector locked notification to the communication network        23. The GSM 31 can lock the gear selector at the same time as        the ABS module 27 engages the hill hold function [STEP 4].    -   iv. Upon receipt of the change notification signal and the gear        selector locked notification, the TCM 25 engages neutral [STEP        6]. The TCM 25 publishes a neutral engaged notification to the        communication network 23.    -   v. Upon receipt of the change notification signal and the        neutral engaged notification, the PCM 29 inhibits throttle        inputs [STEP 7].    -   vi. The TCCM 2 performs a check across all electronic modules to        ensure that the preconditions for a range change are satisfied        [STEP 9]. Provided the preconditions are satisfied, the TCCM 2        completes the range change shift [STEP 10] by outputting a        control signal to control operation of the servo motor in the        transfer case 3. The TCCM 2 also outputs the initialisation        signal to the communications network 3.    -   vii. The TCCM 2 outputs the range change completion signal once        the range change has been completed. In dependence on the range        change completion signal, the TCM 25 will then engage the        correct gear for the new range, or revert back to the state it        was in before the range change shift was initiated [STEP 11].    -   viii. As a safety feature, the ABS module 27 does not remove the        hill hold assist, thereby ensuring that the vehicle does not        roll away once the range change has been completed [STEP 12].    -   ix. Upon receipt of the range change completion signal, the PCM        29 will remove the throttle inhibit [STEP 13].    -   x. Upon receipt of the range change completion signal, the GSM        31 will unlock the shifter [STEP 14].    -   xi. The IPCM 33 outputs a notification signal to display a        message on the instrument cluster informing the driver that the        requested range change has completed, and inform them of the new        selected range [STEP 15].

The ABS module 27 removes the hill hold assist when the throttle pedalis depressed by the driver.

Dynamic Shift (Vehicle Moving)

The control strategy for implementing a dynamic range change will now bedescribed. The control strategy is the same irrespective of whether therange change is from a low range to a high range or vice versa.

-   -   i. The TCCM 2 receives a range change request from the range        change selector 21 [STEP 1]. The TCCM 2 determines whether the        current vehicle state is suitable for a range change. If the        vehicle 5 is not in a suitable state, for example the vehicle        speed is above a low range operating threshold, the IPCM 33        outputs a message [STEP 3] for display on the instrument cluster        advising the driver that the range change cannot be performed.        If the TCCM 2 determines that a range change is possible, the        change notification signal is output to the communications        network 23. In practice, the change notification signal is        generated by changing the value of a communications signal [STEP        2] to indicate that the vehicle is completing a dynamic range        change.    -   ii. The ABS Module 27 receives the change notification signal        over the communication network 23 and engages a control strategy        to prevent the vehicle 5 from accelerating [STEP 4].    -   iii. Upon receipt of the change notification signal and        confirmation that acceleration is inhibited, the GSM 31 locks        the gear selector (shifter) [STEP 5], either mechanically or        through software, to prevent the driver from engaging a gear in        the transmission 7 during the range change. The GSM 31 then        publishes a gear selector locked notification to the        communication network 23.    -   iv. Upon receipt of the change notification signal and the gear        selector locked notification, the TCM 25 engages neutral [STEP        6]. The TCM 25 then publishes a neutral engaged notification to        the communication network 23.    -   v. Upon receipt of the change notification signal and the        neutral engaged notification, the PCM 29 inhibits any throttle        inputs [STEP 7].    -   vi. The TCCM 2 performs a check across all modules to ensure        that the preconditions for a range change are satisfied.        Provided the preconditions are satisfied, the TCCM 2 completes        the range change shift [STEP 9 & 10] by outputting a control        signal to control operation of the servo motor in the transfer        case 3. The TCCM 2 also outputs the initialisation signal to the        communications network 3.    -   vii. The TCCM 2 outputs the range change completion signal once        the range change has been completed. In dependence on the range        change completion signal, the TCM 25 will then engage the        correct gear for the new range, or revert back to the state it        was in before the range change shift was initiated [STEP 11].    -   viii. The ABS module 27 continues to control wheel speed until        the driver intervenes with either throttle or brake pedal input        [STEP 12].    -   ix. Upon receipt of the range change completion signal, the PCM        29 will remove the throttle inhibit [STEP 13].    -   x. Upon receipt of the range change completion signal, the GSM        31 will unlock the shifter [STEP 14].    -   xi. The IPCM 33 outputs a notification signal to display a        message on the instrument cluster informing the driver that the        requested range change has completed, and inform them of the new        selected range [STEP 15].

In the event that the vehicle 5 comes to a standstill during a dynamicrange change, the communications signal previously indicating a dynamicshift would change value to reflect that the static shift strategyshould be implemented to secure the vehicle and prevent it rolling away.

The transfer case range changes can be inhibited under certaincircumstances to prevent the car becoming stranded or to prevent thevehicle rolling away or losing control. For example, dynamic shifts canbe inhibited during wading to prevent the vehicle rolling to a stopmid-wade and thus destroying the bow wave which may be preventing wateringress to the air inlet. Moreover, dynamic shifts can be inhibited whenthe brake temperature is high (for example at high speeds and/ordescending a gradient) since the application of the brakes by the ABSmodule 27 could potentially cause an overheat scenario. The dynamicshifts can be inhibited where the differential is locked (for exampleabove a calibratable limit) in order to prevent loss of stability and/orunintended noise vibration harshness (NVH) effects through the vehicledriveline.

Stored Request for Range Change & Long Press Functionality

The TCCM 2 in combination with the range change selector 21 can provideadditional control functionality, for example to control the timingand/or the trigger events to initiate a range change. At least incertain embodiments, the driver can prime the range change selector 21to trigger the range change through a separate control medium. The TCCM2 can, for example, be configured to implement the range change after adefined time period has elapsed or when one or more vehicle dynamicparameters are satisfied.

This control strategy can be implemented in conjunction with, orindependently of the general control strategy described herein withreference to FIGS. 2 and 3. The operating mode can be implemented in thevehicle 5 having the capability to engage a new range without a customerintervention (i.e. automatically). The range change selector 21 canoperate to provide primary and secondary functions. The differentsequence of events implemented by the primary and secondary functions isspecific to the current operating range of the transfer case, such thatthe TCCM 2 reacts differently if the transfer case 3 is currently in thehigh range or the low range. Alternatively, or in addition, the TCCM 2can be primed to initiate the transfer case range change in dependenceon an alternative trigger.

The control strategy implemented to perform a range change after theTCCM 2 has been primed is illustrated in a second block diagram shown inFIG. 4. The TCCM 2 is primed to perform a range change (B1); and adriver prompt is output to the IPCM 33, for example to display themessage “Range Change Primed” (B2). The range change can subsequently betriggered by the driver operating steering wheel mounted controls (B3).The transfer case 3 performs the range change (B4) in response to thedriver request; and the range change is complete (A5).

In the present embodiment, the primary and secondary functions areselected based on the period of time for which the button is depressed(the “press time”). The press time is monitored by the TCCM 2 anddifferent control strategies are implemented based on the detected presstime. In particular, the press time is compared to a predefined firsttime period which can be calibrated, for example to 1 second, 2 seconds,3 seconds or longer. If the press time is less than the first timeperiod, the primary function is selected. If the press time is longerthan the first time period, the secondary function is selected. Aseparate cancel function can be provided, for example on a steeringwheel control. The range change selector 21 could optionally beconfigured to cancel the primary and secondary functions if the buttonis depressed for a time period longer than a predefined maximum timeperiod. To avoid accidental operation (for example, due to an object inthe vehicle falling on the range change selector 21), the range changeselector 21 could optionally be configured to select the primaryfunction only if the button is depressed for a time period longer than aminimum time period.

The primary function comprises initiating the range change based on thecontrol strategy described herein with reference to FIG. 3. Thesecondary function comprises priming the TCCM 2 ready to initiate therange change when one or more specified criteria are satisfied. When thesecondary function is selected, the vehicle human machine interface(HMI) can display a “primed” status signal (for example on the IPCM 33)and a low range selection light could optionally flash intermittently.The range change selector 21 can optionally be configured automaticallyto cancel the secondary functions if the specified criteria are notsatisfied within a predefined time period.

The primary function implements a control strategy to implement a rangechange without undue delay (subject to the required vehicle operatingparameters being satisfied). Specifically, the TCCM 2 checks the statusof the vehicle 5 by accessing the data published to the communicationsnetwork 23 and, provided the vehicle 5 is in a suitable state (asdescribed herein), outputs a change notification signal to thecommunications network 23.

With reference to the second flow chart 200 shown in FIG. 5, thesecondary function comprises priming the TCCM 2 ready to implement therange change [STEP 201]. The control strategy implemented by thesecondary function depends on the current operating range of thetransfer case, i.e. whether the transfer case is in a high range [STEP203] or in a low range [STEP 202]. The secondary function can compriseinitiating the range change after a predefined time period has elapsed[STEP 206]; and/or when the vehicle speed is above/below a defined speedthreshold [STEP 205]. Alternatively, a range change can be triggered inhigh or low ranges, either with or without a synchroniser [STEP 204]. Inthis arrangement, the driver can implement the range change using asecondary input means, for example in the form of steering wheelcontrols [STEP 208]. The various control strategies are described belowfor a transfer case 3 with and without a synchroniser.

The primary and secondary functions could be selected using differenttechniques. For example, the range change selector 21 could compriseseparate selection means for the respective primary and secondfunctions. For example, the range change selector 21 could comprisefirst and second buttons or switches for selecting the respectiveprimary and secondary functions. Alternatively, the primary andsecondary functions could be selected based on the displacement ortravel of a selection means, or the actuating force applied by the user.A further alternative would be to select the secondary functions if thedriver requests a range change, but the predefined operating conditionshave not been satisfied and the range change selector 21 determines thatthe range change cannot be implemented.

Vehicle Operating in High Range

If the transfer case 3 does not have a synchroniser to low range(requiring static range changes with the vehicle stationary), thesecondary function comprises:

-   -   1. Implementing a time latch to allow the vehicle 5 to change        range automatically if the vehicle 5 satisfies the speed        requirement (i.e. the vehicle comes to rest) within a defined        period of time [STEP 206]. The period of time can be        calibratable, for example by the driver (through the HMI) or can        be predefined (for example by the original equipment        manufacturer OEM).    -   2. Implementing a permanent latch [STEP 207] such that the        vehicle will stay in a primed state for changing range upon        satisfying the speed requirement (i.e. the TCCM 2 determines        that the vehicle speed is zero) at any point in time until the        range change is executed. The latch could be cancelled or        removed, for example by repeating the selection process.

If the transfer case has a synchroniser to low range (permitting“shift-on-the-fly” dynamic range changes), the secondary functioncomprises:

-   -   1. Implementing a time latch [STEP 206] such that the vehicle        will change range automatically after a set period of time. The        period of time could be calibratable, for example by the driver        (through the HMI), or can be predefined (for example by the OEM)        and optionally output to the IPCM 33 for display.    -   2. Implementing a speed latch [STEP 205] such that the vehicle        will change range once a set speed has been ascertained. This        speed could be configurable via the HMI [STEP 211]. In        particular, the driver can define the set speed using        vehicle±cruise control selectors; the HMI; dedicated speed        set±controls [STEP 215]. A transition from a low range to a high        range could be implemented when the vehicle speed is equal to or        greater than a first (upshift) speed threshold; and a transition        from a high range to a low range could be implemented when the        vehicle speed is equal to or less than a second speed threshold.        The first speed threshold can be less that the second speed        threshold. For example, the first speed threshold can be 30 mph        and the second speed threshold can be 50 mph. The first and        second speed thresholds can optionally be predefined by the OEM,        or could be defined by the user.        Vehicle Operating in Low Range

If the transfer case does not have a synchroniser to high range(requiring static range changes with the vehicle stationary), thesecondary function comprises:

-   -   1. Implementing a time latch to allow the vehicle to change        range automatically if the vehicle satisfies the speed        requirement (i.e. the vehicle comes to rest) within a defined        period of time. The period of time can be calibratable, for        example by the driver (through the HMI), or can be predefined        (for example by the OEM).    -   2. Implementing a permanent latch [STEP 207] such that the        vehicle will stay in a primed state for changing range upon        satisfying the speed requirement at any point in time until the        range change is executed. The latch could be cancelled or        removed, for example by repeating the selection process.

If the transfer case has a synchroniser to high range (permitting“shift-on-the-fly” dynamic range changes), the secondary functioncomprises:

-   -   1. Implementing a time latch [STEP 206] such that the vehicle        will change range automatically after a set period of time. The        period of time could be calibratable, for example by the driver        (through the HMI), or can be predefined (for example by the OEM)        and optionally output to the IPCM 33 for display.    -   2. Implementing a speed latch [STEP 205] such that the vehicle        will change range once a set speed has been ascertained. This        speed could be configurable via the HMI [STEP 211], for example        using the steering wheel mounted control for setting a cruise        control set speed and/or automatic speed limiter set speed.

The TCCM 2 outputs the control signal to control the transfer case 3 toimplement the requested range change once the relevant criteria aresatisfied [STEP 213]. The TCCM 2 can implement the range change withoutfurther input from the driver when the relevant criteria are satisfied.Alternatively, when the relevant criteria are satisfied, the TCCM 2 canoutput a prompt seeking confirmation from the driver that the rangechange is to be implemented.

The primary and secondary functions could be selected based on theperiod of time for which an actuator is held in a predefined position,for example against a stop. The primary function could be selected bydisplacing the actuator to the predefined position; and the secondaryfunction could be selected by holding the actuator in said predefinedposition for a time period longer than the first time period describedherein. The actuator could be spring-biased away from the predefinedposition, for example to a neutral position. The actuator could, forexample, be a lever, a switch or a rotary knob.

It will be appreciated that, at least in certain embodiments, the rangechange selector 21 can enable both the primary and secondary functionsto be selected using a single selection device, such as a button. Thisdual function could optionally be supplemented with a further controldevice, such as a touchscreen, a touch-panel or a rotary selector, toprovide additional control functions. For example, the range changeselector 21 could be configured to activate a control screen tocalibrate related functionality. For example, the control screen couldallow the locking torque of a differential to be adjusted. A sliderdisplayed onscreen (or other soft input device) could be used to adjustthe locking torque. This function is believed to be patentableindependently of the other techniques described herein.

Trailer Tow Mode Interface & Hill Climb Assist

The TCCM 2 can operate to provide trailer towing and/or hill climbassist functionality. At least in certain embodiments, this operatingmode can improve the driver's control when setting off with a trailercoupled to the vehicle 5 or when travelling up an incline. A trailerconnected signal is published to the communications network 23 when atrailer socket is connected to the vehicle. The TCCM 2 checks thetrailer connected signal and, upon determining that a trailer has beenconnected, generates a driver prompt to engage the transfer case lowrange. The driver prompt is published to the communications network 23and can be displayed on the IPCM 33, for example. The driver can acceptor dismiss the recommendation, for example by operating the range changeselector 21 or steering wheel controls. Conversely, when the trailer isremoved, the TCCM 2 can output a recommendation to engage the transfercase high range. The recommendation could again be published to thecommunications network 23 for display on the IPCM 33.

The control strategy implemented by the TCCM 2 when the vehicle 5 isstatic is illustrated in a third block diagram shown in FIG. 6A. TheTCCM 2 detects a trailer connected signal over the communicationsnetwork indicating that a trailer is connected to the vehicle 5 (C1).The TCCM 2 outputs a driver prompt to the IPCM 33, for example todisplay the message “Trailer detected, suggest low range engage” (C2).The driver can then implement the range change from high to low usingthe range selector means 21, for example disposed on the steering wheel(C3). The TCCM 2 continues to monitor the vehicle speed and once aconstant speed has been detected, a driver prompt is output to the IPCM33, for example to display the message “Pull away complete. Suggest highrange engaged.” (C4). The driver can then implement the transfer caserange change from low to high using the range selector means 21 (C5).

The control strategy implemented by the TCCM 2 when the vehicle 5 ismoving is illustrated in a fourth block diagram shown in FIG. 6B. TheTCCM 2 detects a trailer connected signal over the communicationsnetwork indicating that a trailer is connected to the vehicle 5 (D1).The TCCM 2 outputs a driver prompt suggesting that the driver stop andengage low range for towing a calibratable rolling resistance (D2). Thedriver can then implement the range change from high to low using therange selector means 21, for example disposed on the steering wheel,when the vehicle 5 has stopped (D3). The TCCM 2 continues to monitor thevehicle speed and once a constant speed has been detected, a driverprompt is output to the IPCM 33, for example to display the message“Pull away complete. Suggest high range engaged” (D4). The driver canthen implement the transfer case range change from low to high using therange selector means 21 (D5).

A range change request signal is received from the range change selector21 in response to a driver request (A1). Upon receive of the rangechange request signal over the communications network 23, the TCM 25and/or the GSM 31 request neutral in the transmission 7; the GSM 31inhibits gear selection; the PCM 29 inhibits throttle pedal input; andthe ABS control module 27 applies the brakes and/or controls wheel speed(A2). The transfer case 3 then performs the range change (A3). The TCM25 engages an appropriate gear; the GSM 31 permits gear selection; andthe PCM 29 enables throttle pedal inputs (A4). The range change is thencomplete (A5).

A calibratable speed threshold can optionally be set at which the TCCM 2prompts the driver to engage high range. The TCCM 2 can, for example,monitor the vehicle speed and output the prompt once the vehicle 5 ismoving at a constant speed; or a high enough vehicle speed has beendetected that low range is no longer necessary. The speed thresholdcould be set through the use of steering wheel mounted controls, orthrough the use of the range change selector 21. This functionalitycould also be incorporated into the low range V_(max) upshift discussedherein.

This control strategy can be implemented in conjunction with, orindependently of the general control strategy described herein withreference to FIGS. 2 and 3. The TCCM 2 checks the communication network23 for a towing signal indicating that a trailer is connected to thevehicle 5. Alternatively, or in addition, the TCCM 2 (or other controllogic) can monitor one or more of the following: powertrain torque,vehicle orientation and acceleration to determine if high torque isrequired for running. The high torque requirement can in itself providea suitable indicator that the vehicle 5 is towing a trailer.

Upon detection of a positive towing signal or an overly heavy load uponthe powertrain, the TCCM 2 outputs a driver prompt recommending that thetransfer case low range is engaged to provide improved vehicle control.The driver prompt can, for example, be output to the driver as a messagethrough the High Level Display Front (HLDF) or the IPCM 33. In responseto the prompt, the driver can implement the range change either throughthe use of steering wheel mounted controls or the range change selector21 (utilising the primary or secondary function described herein). Therange change function is the same irrespective of whether the driveruses the steering wheel mounted controls or the range change selector 21to implement the range change. The message can be dismissed, for exampleusing the steering wheel controls.

When in low range and cruising at a (steady-state) speed after settingoff with a trailer, the TCCM 2 prompts the driver to engage high range.The cruising speed can be calibratable, for example by the driver or theOEM. This functionality can optionally be inhibited if the vehicle isoperating in an off-road mode. The prompt can, for example, be output tothe driver as a message through the High Level Display Front (HLDF) orthe IPCM 33. In response to the prompt, the driver can implement therange change either through the use of steering wheel mounted controlsor the range change selector 21 (utilising the primary functionassociated therewith). The range change function is the sameirrespective of whether the driver uses the steering wheel mountedcontrols or the range change selector 21 to implement the range change.The message can be dismissed, for example using the steering wheelcontrols.

The TCCM 2 can also monitor the communications network 23 to determinethe vehicle orientation (which can, for example, be measured by one ormore gyroscopes and/or accelerometers disposed on the vehicle). If thevehicle orientation exceeds a defined threshold, the TCCM 2 determinesthat the vehicle 5 is on a steep incline and outputs a prompt to thedriver to engage low range. Again, the TCCM 2 could determine that thevehicle is starting off on an incline based on the powertrain torquerequired to displace the vehicle.

Low Range V_(max) Upshift

The TCCM 2 can operate to change from a low range to a high range basedon the vehicle speed and/or acceleration. This operating mode allows theTCCM 2 to change range automatically during hard acceleration or as thespeed of the vehicle approaches that of the maximum speed capability inlow range. The TCCM 2 can be configured automatically to change from lowrange to high range when the acceleration rate of the vehicle results inthe low range V_(max) (i.e. the maximum permitted vehicle speed when thelow range is engaged) being reached or exceeded. The TCCM 2 can alsoprovide a calibratable speed at which the vehicle will automaticallyperform a change from low range to high range depending on varioussignals received over the communications network 23.

The control strategy implemented by the TCCM 2 is illustrated in a fifthblock diagram shown in FIG. 7. The TCCM 2 detects that the transfer case3 is operating in a low range (E1). The TCCM 2 monitors vehicleacceleration and determines when the vehicle speed is equal to orgreater than a maximum low range speed V_(MAX) (E2). The TCCM 2 outputsa driver prompt to the IPCM 33 to recommend that high range is engaged,either by the steering wheel controls or the range selector means 21(E3). The driver can then implement the range change from low to highusing the range selector means 21 (E4). The TCCM 2 could alternativelybe configured to implement an automated range change by checking thecalibration parameters (E5); and, provided these are satisfied,performing an automated transfer case upshift from low range to highrange (E6). The transfer case 3 can perform the upshift automaticallywithout the need for driver input (E4).

The TCCM 2 can also implement an automated shift into high range when akickdown switch on the throttle pedal is activated. The TCCM 2 can beconfigured to detect a kickdown signal over the communications network23 when the kickdown switch is activated. This operating mode would alsoplay a role in the functional safety of the system, allowing anautomatic shift to high range to increase the maximum speed of thevehicle, for example when the driver forgets that they are in low rangeand accelerates onto a high speed road.

This control strategy can be implemented in conjunction with, orindependently of the general control strategy described herein withreference to FIGS. 2 and 3. This operating mode is illustrated in thethird flow diagram 300 shown in FIG. 8. The TCCM 2 determines that thetransfer case 3 is in a low range [STEP 302]. The TCCM 2 is configuredto monitor vehicle acceleration, vehicle speed and throttle position toassess how aggressively the driver is driving [STEP 303]. When in lowrange, these parameters can be monitored to predict the point at whichthe vehicle will reach a maximum speed threshold for low range [STEP301]. When the vehicle 5 is at or near this maximum speed threshold theTCCM 2 can output information to the IPCM 33 [STEP 307] to prompt thedriver to change from low range to high range. The driver can implementthe range change using the range change selector 21 to implement theprimary or secondary functions described herein [STEP 310].

The driver can dismiss the information displayed on the IPCM 33 [STEP311]. Alternatively, the driver can operate the range change selector 21to implement the range change [STEP 312]. In response to the user input,the TCCM 2 initiates the range change.

A secondary upshift means could be identified, such as the kickdownswitch [STEP 308] on the throttle pedal. The TCCM 2 can be configured toimplement the range change when the kickdown switch is operated. Thepoint at which this behaviour is effective could be calibrated so as notto interfere with the intent to change down a number of gears tomaximise acceleration.

Alternatively, a timing method could be employed such that if a certainamount of throttle were seen over a given period of time then thevehicle would shift to high range. This would also be calibratable toshow the intent of the driver to accelerate even though they havereached the maximum velocity in low range.

Engine Start Range Check

This operating mode automatically checks whether low range is requiredwhen the engine is started. This mode can assist the driver to selectthe appropriate transfer case range after having driven the vehicle 5off-road or after a trailer is decoupled. The range change can, forexample, be implemented through the use of range change selector 21 orthe steering wheel controls.

This control strategy can be implemented in conjunction with, orindependently of the general control strategy described herein withreference to FIGS. 2 and 3. This operating mode is illustrated in thefourth flow diagram 400 shown in FIG. 9. The TCCM 2 detects an engineignition signal over the communications network [STEP 401]. The TCCM 2monitors the current transfer case range [STEP 402] and the vehicleoperating mode currently active in the ATCM 35 [STEP 403]. If thetransfer case low range is engaged and the vehicle operating mode isconfigured for transfer case high range (for example the ATCM 35 isoperating in a Road/Dynamic mode), the TCCM 2 outputs a driver promptupon detection of the ignition cycle [STEP 404]. The driver promptrecommends that the transfer case high range is engaged. The prompt can,for example, take the form of a message displayed on the IPCM 33. Thedriver makes the appropriate input [STEP 405]. To perform the rangechange, the driver can activate the range change selector 21 to providethe primary or secondary functions described herein [STEP 407].

The message can optionally be dismissed [STEP 406] by the driver, forexample through the use of the steering wheel mounted controls. The TCCM2 would inhibit output of the prompt if the ATCM 35 is in an operatingmode which defaults to the transfer case low range (for example anoff-road mode, such as rock crawl)..

Vehicle Operating Mode Interface

The TCCM 2 can be integrated with other vehicle systems, such as theATCM 35 for engaging different vehicle operating modes, such as: RockCrawl; Mud; Sand; Grass/Gravel/Snow; Road; and Dynamic. Some of thevehicle operating modes (such as Rock Crawl) can optionally beconfigured to require that the transfer case operates in a low range.Conversely, some of the vehicle operating modes can optionally beconfigured to require that the transfer case operates in a high range.Some or all of the vehicle operating modes can have a preferred transfercase operating range which is not essential. For example, the Mud, Sandand Grass/Gravel/Snow operating modes can be optimised for operation inthe transfer case low range; and the Road and Dynamic operating modescan be optimised for operation in the transfer case high range. In thepast, the driver would have been required manually to engage theappropriate transfer case range based on the selected vehicle operatingmode.

If the transfer case high range is engaged, the TCCM 2 is configuredautomatically to engage low range when a vehicle operating moderequiring low range is selected (either by the driver or automatically).The TCCM 2 can engage low range 1 after a period of time has elapsed(the period of time can optionally be calibrated by the driver or theOEM). When a different vehicle operating mode is selected, for exampleone optimised for operation in the transfer case high range, the TCCM 2can prompt the driver to confirm whether they still require low range.At least in certain embodiments, when an operating mode is selectedwhich requires the transfer case high range, the TCCM 2 canautomatically engage the transfer case high range, for example inanticipation of a higher speed driving.

This control strategy can be implemented in conjunction with, orindependently of the general control strategy described herein withreference to FIGS. 2 and 3. This operating mode is applicable to avehicle 5 operable in different modes which alter the response of thevehicle characteristics (such as performance, driveability anddynamics). One or more of the vehicle operating modes can require (orwould be complemented by) engagement of the transfer case low range, forexample to aid traction. The vehicle operating modes can broadly beclassified as off-road modes and on-road modes. The off-road modes canfurther be classified as low-range off-road modes (i.e. off-roadoperating modes which require or are complemented by selecting lowrange) and high-range off-road modes (i.e. off-road operating modeswhich do not require selection of the low range). In the presentembodiment, the low-range off-road modes are Rock Crawl and Mud; and thehigh-range off-road modes are Sand and Grass Gravel Snow (GGS). In thepresent embodiment, the on-road modes, such as Road and Dynamic, areusually selected when the vehicle will be driving at speeds above thatallowed in the transfer case low range (and when improved fuel economyis required) so the transfer case high range is typically engaged. Thevehicle operating modes can be selected by the driver, for examplethrough the HMI, or automatically by the vehicle 5. The TCCM 2 accessesthe communications network 23 to determine which vehicle operating modeis currently selected and accesses a look-up table to determine whetherthe selected vehicle operating mode is a low-range off-road mode or ahigh-range off-road mode.

This operating strategy for integrating the TCCM 2 with the ATCM 35 isillustrated in a sixth block diagram shown in FIG. 10. The ATCM 35 isoperated to select a Rock Crawl mode (F1) and the low range isautomatically engaged (F2). If the ATCM 35 is subsequently operated toselect a Road mode (F3), the TCCM 2 controls the transfer case 3automatically to select the high range (F4). If the ATCM 35 is operatedto select an off-road mode other than Rock Crawl (F5), a prompt isoutput to the IPC 33 to display the message “Low Range Required?” (F6).If a Road mode is subsequently selected (F7), the TCCM 2 controls thetransfer case 3 to engage the high range (F4).

This control mode will now be described with reference to a fifth flowchart 500 shown in FIG. 11 (the selected high/low range of the transfercase 3 is illustrated in the right hand column). When engaging alow-range off-road operating mode, the TCCM 2 starts a timer beforeautomatically engaging low range. When disengaging that vehicleoperating mode, the TCCM 2 automatically engages a transfer case highrange.

When the transfer case low range is engaged [STEP 501], the TCCM 2implements the following control logic:

-   -   i. The TCCM 2 will not engage the high range if a low-range        off-road operating mode is disengaged [STEP 502] and another        off-road operating mode is selected [STEP 503] (irrespective of        whether the newly selected operating mode is a high-range or a        low-range off-road operating mode).    -   ii. The TCCM 2 will engage the high range if an on-road vehicle        operating mode is selected [STEP 505].    -   iii. If an on-road mode is engaged indirectly after a low-range        off-road operating mode, the TCCM 2 will engage high range [STEP        504].    -   iv. If a high-range off-road operating mode is engaged then the        TCCM 2 will not shift to low range unless requested to do so by        the driver.

The high range is engaged [STEP 507] and the range change is thencompleted [STEP 506].

When the transfer case high range is engaged [STEP 507], the TCCM 2implements the following control logic:

-   -   i. The TCCM 2 remains in the high range if the vehicle operating        mode changes from an on-road operating mode [STEP 508] to a        high-range off-road operating mode [STEP 509].    -   ii. The TCCM 2 will engage the low range if a low-range off-road        operating mode is engaged [STEP 510].

The high range is engaged [STEP 513] and the range change is thencompleted [STEP 512].

The TCCM 2 will not automatically change range (from high to low range;or from low to high range) when the vehicle operating modes change basedon automated control logic.

Furthermore, the TCCM 2 can be configured to inhibit range changes ifthe range change would result in a reduction in the output (drive)torque. A transfer case upshift typically results in a decrease in theengine speed which can result in a corresponding reduction in the outputtorque, particularly for a petrol internal combustion engine.

It will be appreciated that various changes and modifications can bemade to the present invention without departing from the scope of thepresent application. Further aspects of the present invention will nowbe set out in the accompanying numbered paragraphs:

-   1. A vehicle control apparatus for controlling a vehicle transfer    case operable in a high range and a low range; the vehicle control    apparatus comprising:    -   a range change selector for selecting first and second control        strategies for said transfer case;    -   wherein the range change selector is operable to select said        first and second control strategies based on an activation time        of said range change selector.-   2. A vehicle control apparatus as described in paragraph 1, wherein    the first control strategy is selected if the activation time is    less than a predefined time threshold; and the second control    strategy is selected if the user activation time is greater than    said predefined time threshold.-   3. A vehicle control apparatus as described in paragraph 1, wherein    the first control strategy implements a concurrent transfer case    range change.-   4. A vehicle control apparatus as described in paragraph 1, wherein    the second control strategy implements a deferred transfer case    range change.-   5. A vehicle control apparatus for controlling a vehicle transfer    case operable in a high range and a low range; wherein the control    system is operable to implement a deferred transfer case range    change.-   6. A vehicle control apparatus as described in paragraph 5, wherein    the control system is configured to implement the deferred transfer    case range change when one or more vehicle operating conditions are    satisfied.-   7. A vehicle control apparatus as described in paragraph 6, wherein    said one or more vehicle operating conditions comprise vehicle speed    and/or vehicle acceleration.-   8. A vehicle control apparatus as described in paragraph 7, wherein    the deferred transfer case range change is implemented when the    vehicle speed exceeds a predefined speed threshold; and/or the    vehicle acceleration exceeds a pre-defined acceleration threshold.-   9. A vehicle control apparatus as described in paragraph 8, wherein    the speed threshold is pre-defined; or the speed threshold is user    defined.-   10. A vehicle control apparatus as described in paragraph 6, wherein    said one or more vehicle operating conditions comprise an operating    range of the vehicle transmission.-   11. A vehicle control apparatus as described in paragraph 10,    wherein the deferred transfer case range change is implemented when    the vehicle transmission engages neutral.-   12. A vehicle control apparatus as described in paragraph 5, wherein    the control system is configured to implement the deferred range    change after a pre-defined period of time has elapsed.-   13. A vehicle control apparatus as described in paragraph 5, wherein    the control system is operable to cancel the deferred transfer case    range change when an activation procedure is repeated.-   14. A method of controlling a vehicle transfer case operable in a    high range and a low range; the method comprising selecting first    and second control strategies for said transfer case based on an    activation time of a range change selector.-   15. A method as described in paragraph 14, wherein the first control    strategy is selected if the activation time is less than a    predefined time threshold; and the second control strategy is    selected if the user activation time is greater than said predefined    time threshold.-   16. A method as described in paragraph 14, wherein, when the first    control strategy is selected, the transfer case range change is    implemented concurrently.-   17. A method as described in paragraph 14, wherein, when the second    control strategy is selected, implementation of the transfer case    range change is deferred.-   18. A method of controlling a vehicle transfer case operable in a    high range and a low range; the method comprising priming a vehicle    control apparatus to implement a deferred transfer case range    change.-   19. A method as described in paragraph 17, wherein the method    comprises implementing the deferred transfer case range change when    one or more vehicle operating conditions are satisfied.-   20. A method as described in paragraph 19, wherein said one or more    vehicle operating conditions comprise vehicle speed and/or vehicle    acceleration.-   21. A method as described in paragraph 20 comprising implementing    the deferred transfer case range change when the vehicle speed    exceeds a predefined speed threshold; and/or the vehicle    acceleration exceeds a pre-defined acceleration threshold.-   22. A method as described in paragraph 21, wherein the speed    threshold is pre-defined; or the speed threshold is user defined.-   23. A method as described in paragraph 17, wherein said one or more    vehicle operating conditions comprise an operating range of the    vehicle transmission.-   24. A method as described in paragraph 23 comprising implementing    the deferred transfer case range change when the vehicle    transmission engages neutral.-   25. A method as described in paragraph 18 comprising implementing    the deferred range change after a pre-defined period of time has    elapsed.-   26. A vehicle comprising a vehicle control apparatus as described in    paragraph 1.

The invention claimed is:
 1. A vehicle control system for controlling avehicle transfer case operable in a high range and a low range, thevehicle control system comprising: a selector that is operable by a userto indicate a range change request; and a controller comprising one ormore processors configured to execute computer readable code to causethe vehicle control system to in response to a range change request fromthe selector, select one of a first control strategy and a secondcontrol strategy based on a user activation time of the selector,wherein the first and second control strategies are strategies forimplementing a transfer case range change from one of the high range orthe low range to the other of the high range or the low range.
 2. Avehicle control system as claimed in claim 1, wherein the first andsecond control strategies are further strategies for implementing atransfer case range change from said other of the high range or the lowrange to said one of the high range or the low range.
 3. A vehiclecontrol system as claimed in claim 1, wherein the selector comprises ahuman machine interface.
 4. A vehicle control system as claimed in claim1, wherein the first control strategy is selected if the user activationtime is less than a predefined time threshold and the second controlstrategy is selected if the user activation time is greater than saidpredefined time threshold.
 5. A vehicle control system as claimed inclaim 1, wherein the first control strategy implements a concurrenttransfer case range change and the second control strategy implements adeferred transfer case range change.
 6. A vehicle control system asclaimed in claim 1, wherein the second control strategy implements adeferred transfer case range change and the control system is configuredto implement the deferred transfer case range change when one or morevehicle operating conditions are satisfied or after a pre-defined periodof time has elapsed.
 7. A vehicle control system as claimed in claim 6,wherein said one or more vehicle operating conditions comprise at leastone of vehicle speed, vehicle acceleration and when a vehicletransmission of the vehicle engages neutral.
 8. A vehicle comprising avehicle control system as claimed in claim
 1. 9. A vehicle controlsystem for controlling a vehicle transfer case operable in a high rangeand a low range, the control system comprising a controller comprisingone or more processors configured to execute computer readable code tocause the vehicle control system to implement a concurrent transfer caserange change in response to a range change request if a first controlstrategy is selected; and implement a deferred transfer case rangechange in response to the range change request if a second controlstrategy is selected.
 10. A vehicle control system as claimed in claim9, wherein the deferred transfer case range change is implemented whenat least one of a vehicle speed exceeds a predefined speed threshold anda vehicle acceleration exceeds a pre-defined acceleration threshold. 11.A vehicle control system as claimed in claim 9, wherein the controlleris configured to implement the deferred transfer case range change whenone or more vehicle operating conditions are satisfied.
 12. A vehiclecontrol system as claimed in claim 9, wherein the control system isoperable to cancel the deferred transfer case range change when anactivation procedure for making a range change request is repeated. 13.A method of controlling a vehicle transfer case operable in a high rangeand a low range, the method comprising in response to a range changerequest from a selector, selecting one of a first control strategy and asecond control strategy based on a user activation time of the selector,wherein the first and second control strategies are strategies forimplementing a transfer case range change from one of the high range orthe low range to the other of the high range or the low range.
 14. Amethod as claimed in claim 13, wherein the first and second controlstrategies are further strategies for implementing a transfer case rangechange from said other of the high range or the low range to said one ofthe high range or the low range.
 15. A method as claimed in claim 13,wherein the selector comprises a human machine interface.
 16. A methodas claimed in claim 13, wherein the first control strategy is selectedif the user activation time is less than a predefined time threshold;and the second control strategy is selected if the user activation timeis greater than said predefined time threshold.
 17. A method as claimedin claim 13, wherein, when the first control strategy is selected, thetransfer case range change is implemented concurrently and when thesecond control strategy is selected, implementation of the transfer caserange change is deferred.
 18. A method as claimed in claim 13, whereinwhen the second control strategy is selected, implementation of thetransfer case range change is deferred and the method comprisesimplementing the deferred transfer case range change when one or morevehicle operating conditions are satisfied or after a pre-defined periodof time has elapsed.
 19. A method as claimed in claim 18, wherein saidone or more vehicle operating conditions comprise at least one of avehicle speed and a vehicle acceleration.
 20. A method as claimed inclaim 19, comprising implementing the deferred transfer case rangechange when at least one of the vehicle speed exceeds a predefined speedthreshold and the vehicle acceleration exceeds a pre-definedacceleration threshold.
 21. A method as claimed in claim 18, comprisingimplementing the deferred transfer case range change when a vehicletransmission associated with the transfer case engages neutral.